Crusher with variable opening screen grate



Jan. 18, 1966 A. B. HANSE ETAL 3,229,919

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United States Patent 3,229,919 CRUSHER WITH VARIABLE OPENING SCREEN GRATE Albert B. Hanse and Leonard N. Kint, Cedar Rapids, Iowa, assignors to Pettibone Mulliken Corporation, a corporation of Delaware Filed June 15, 1962, Ser. No. 202,870 13 Claims. (Cl. 241-86) The present invention relates to a screen grate for an apparatus for crushing rock or the like.

The present invention was devised for use with a rock crusher of the type wherein an impeller rotating about a generally horizontal axis throws rock against a screen grate. The rock is fractured either by impacting against hammers on the impeller, against the screen grate, or both. In addition to serving as an impacting member, the screen grate to a large measure serves to determine the size of the crushed rock. The grate has impacting bars with spaces therebetween. Thus rocks smaller than the spaces between the bars will pass through the spaces (unless directed at the bars themselves) so that the rock then will leave the machine. Larger rock will impact against the bars and may be fractured, but in any event will rebound or fall back into the path of the hammers.

Some operators of rock crushers find it necessary from time to time to produce rock of greater or smaller maximum dimensions than that which they have been producing in the past. These changes of course result from different demands by customers, etc. In the past it has been a laborious job to change the grates on a crusher of the type refer-red to so that changes in rock size would be achieved. The grates in commercial use are a single unit. In order to obtain a different grate opening it is necessary that the existing grate be removed and a new grate having the desired bar spacing be substituted for the one that was removed. The grates are large and unwieldly. They are securely fixed in place since they are often employed to provide structural rigidity to the crusher.

We have devised a grate structure for rock crushers, particularly those of the type mentioned, which enables the operator of the machine to change the bar spacing with relatively little efiort as compared to the work required in the changing of the grates of the present commercial machines. At the same time the structure We have devised does not sacrifice the aid to the structural rigidity of the machine that is supplied by the screen grate. A further feature of our invention is that the mounting members and bolts, or the like, employed to secure and position the grate bars are substantially protected from damage by impacting rock. The mounting structure will not be worn away with one setting of the grate bars to an extent that would impair or prevent the mounting of the grate bars at another setting.

Further objects and advantages of the present invention will be apparent from the following description taken in conjunction with the drawings in which:

FIGURE 1 is a perspective view of a crusher of the type in which the present invention can suitably be incorporated, with portions of the enclosure removed to better illustrate the present invention;

FIGURE 2 is an enlarged view of a portion of the grate support or frame as viewed in FIGURE 1 but with the grate bars not in place;

FIGURE 3 is a section taken at line 33 of FIGURE 2;

FIGURE 4 is a view corresponding to FIGURE 3, but illustrating the grate bars mounted in the supporting frame;

FIGURE 5 is a view of a portion of the grate, as viewed in FIGURE 1, with some of the grate bars mounted therein and with portions of some in section;

3,229,919 Patented Jan. 18, 1966 "ice FIGURE 6 is a section through a top spacer as viewed at line 6-6; and

FIGURE 7 is a view corresponding to FIGURE 6 of an alternative top spacer for use when five grate bars per side are employed.

Although the following disclosure offered for public dissemination is detailed to ensure adequacy and aid understanding, this is not intended to prejudice that purpose of a patent which is to cover each new inventive concept therein no matter how others may later disguise it by variations in form or additions or further improvements. The claims at the end hereof are intended as the chief aid toward this purpose; as it is these that meet the requirement of pointing out the parts, improvement, or combinations in which the inventive concepts are found.

FIGURE 1 illustrates a crusher having an enclosure generally 10 which serves as the frame for the machine. The top and front of the frame or enclosure 10 has been removed from the machine as it is viewed in FIGURE 1. A shaft 11 is journaled in frame 10 and is disposed in an approximately horizontal position between side walls 12 and 13 of the frame. An impeller 14 is secured to shaft 11 and is rotated by a power means, not shown, connected to the shaft. The direction of rotation is such that the top of impeller 14, as viewed in FIGURE 1, is moved away from the viewer. A plurality of hammers 15 are secured to impeller 14. The rock to be crushed is dropped into the path of hammer 15 generally at or near the top of the impeller. The structure for introducing the rock is not illustrated but can be of a conventional nature. The impeller with its hammers throws the rock or its fragments in the general direction of the screen grate generally 16, usually performing the major rock breaking by reason of the impacts between the moving hammers and the rock.

Grate 16 comprises a generally rectangular main support 18 having two side members 19, a center vertical member 20, a center horizontal member 21, a top member 22 and a bottom member 23. Side members 19 have a plurality of pads 24 which abut side walls 12 and 13. Bolt holes 25 (FIGURE 2) extend through side members 19 and pads 24. Bolts, not shown, are inserted through bolt holes 25 and corresponding openings in sides 12 and 13 to secure the main support 18 to the frame of the machine. Main support 18 is a unitary member which may be formed as a casting. When bolted to sides 12 and 13, it acts as a rigid support or brace between those sides to prevent them from buckling or being bent even though they are not externally braced.

Between side members 19 and center member 20 are positioned a plurality of grate bars 28. The number and spacing of the grate bars 28 will depend upon the preferences of the operator. At the bottom, each grate bar has a truncated triangular shaped head 29. Bottom member 23 of the main support 18 has a slot 30 ateach side of the center extending behind and parallel to the front face of the main support. In cross section, slot 30 has a truncated triangular configuration corresponding to that of the bottom heads 29 of the grate bars. Heads 29 are received and wedged into slot 30 by the truncated triangular configuration of each.

At each side of center vertical member 20 the center horizontal member 21 has a slot 32 therein. A center spacer plate 33 having a plurality of abutments 34 thereon is positioned over front face of the center horizontal member 21. Abutments 34 project outwardly at each side of the grate bars 28. At the rear face of each grate bar there is an opening 35 aligned with slots 32 and terminating in a pocket 36 extending transversely through the grate bar. Spacer plates 33 have openings 37 centered between abutments 34. Bolts 38 are inserted from the rear through slots 32, openings 37 and openings 35, and are threaded onto nuts 39 positioned in pockets 36.

Top member 22 forms a flange 41 at each side of center member 20. Each of flanges 41 have three bolt holes 42 therethrough. A top spacer plate 43 overlies each of flanges 41. Spacer plate 43 has a plurality of abutments 44 projecting forwardly thereon. Across the top, spacer plate 43 has a series of Openings 45 aligned with bolt holes 42 in flanges 41.

A wedge on locking bar 47 is employed at each side of center member 20. The top of wedge 47 abuts the bottom side of upper flange 48 of top member 22. The bottom of Wedge 47 has a tapered face 49. The upper ends of grate bars 28 have a correspondingly tapered face 50 facing somewhat forwardly. Aligned with bolt holes 42 are three slots 51 in the top of each of wedges 47. Slots 51 terminate in slotted pockets 52. Bolts 53 have their heads 54 in pockets 52 and extend through slots 51, openings 45 and bolt holes 42. Nuts 55 are threaded onto the back of bolts 53.

It will be noted that in FIGURE three grate bars are used per side. Therefore the center'spacer plate 33 has four abutments 34. In FIGURE 1 there are four grate bars per side. As a consequence, top spacer plate 43' of FIGURE 1 has five abutments 44' thereon. Similarly, center, spacer plate 33' has five abutments 34 as a part thereof. FIGURE 7 illustrates a top spacer plate 43" having six abutments 44" thereon. Top spacer plate 43" would be used in place of spacer plate 43 when it was desired to have five grate bars 28 per side. At the same time a center spacer plate corresponding to plate 33 would be employed except that it likewise would have six abutments thereon.

If, for example, the operator desired to change from three grate bars per side as illustrated in FIGURE 5 to four grate bars per side as illustrated in FIGURE 1, he would loosen and remove bolts 53 along with wedges 47. Thereafter by loosening and removing bolts 38, each of grate bars 28 may be lifted up and out of the main support 18. When these bolts are in place, even though the nuts 39 are not thereon, the grate bars 28 may not be moved upwardly to Withdraw heads 29 from slot 30. After substituting spacer plates 33 and 43' for spacer plates 33 and 43, four grate bars per side would be reinserted. The first step of course would be to slip head 29 into slot 30. Thereafter bolts 38 would be re-inserted and secured in place. The two wedges 47 then would be fastened in place with the six bolts 53.

Fingers 58 project downwardly from bottom member 23. The use of such fingers is conventional. In some crushers they may be dispensed with entirely and in others, alternatives may be substituted therefor. Our invention may be used with any such variations.

The term rock as used herein is employed to not only apply to natural stone, but also to such other materials of similar characteristics which one might wish to crush in a machine of the general type described. An example of such other material would be slag.

We claim:

1. A deflector screen grate for an apparatus for breaking rock or the like, said grate including: a frame means comprising a horizontal top support, a horizontal intermediate support, and a horizontal bottom support, said bottom support having a front face and spaced walls rearwardly of said face defining an upwardly facing slot parallel to and rearwardly .of said face, said intermediate support having a front face with a slot extending through said support from front to back, said latter slot being elongated in the .direction normal to the front to back direction and parallel to the slot in the bottom support, said top support having a front face and an abutment extending forwardly of said face and above said face, said top support having bolt openings therethrough from front to back; top spacer means including a plate in juxtaposition to said top support face and having a plurality of pairs of spaced abutments projecting forwardly therefrom; an intermediate spacer means in jux- 43 taposition to said intermediate support face and having a plurality of pairs of correspondingly spaced abutments projecting forwardly therefrom; a plurality of grate bars positioned transversely to said supports, between the spacer means and extending forwardly of the spacer means, each bar being between a pair of abutments respectively with the sides of the bar being approximately in contact with the abutments, the bars each having a bottom and engaged in the slot on the bottom support, each bar having a pocket therein forwardly of the slot in the intermediate support, and a bolt opening from said pocket to said slot;

bolts extending through the slotof the intermediate support, said opening and into the pocket; nuts in said pockets,

and secured on said bolts; a top locking bar abutting against a forwardly facing part of the grate bars at the top thereof and against said abutment; bolts secured in said locking bar and extending rearwardly through the bolt openings; and a nut secured to the latter bolts rearwardly of the top support. i

2. A grate as set forth in claim 1, wherein the top spacer means has bolt openings therethrough corresponding in alignment to the bolt openings in the top support, and the last mentioned bolts extend through the bolt openings in the top spacer means.

3. A grate as set forth in claim 1, wherein at least one of said walls tapers downwardly toward the other wall, and the bottoms of the grate bars are correspondingly tapered whereby said grate bars are wedged into the slot in the bottom support.

4. A grate as set forth in claim 1,wherein the spacer means includes two top spacers, on one of which the pairs of abutments are spaced one distance from the adjacent abutments and on the other of which the pairs of abutments are spaced a second distance from the adjacent abutments; and two intermediate spacers, on one of which the pairs of abutments are spaced one distance from the adjacent abutments and on the other of which the pairs of abutments are spaced a second distance from the adjacent abutments; whereby using said one of each pair of spacers the grate bars are a first distance apart and using said otherspacers the grate bars area second distance apart.

5. In a crusher for rock or the like comprising walls defining a breaking chamber, a deflector screen grate in said chamber, and an impeller in said chamber extending between two walls and rotating in a given direction about a generally horizontal axis to throw rock against said grate, the improvement in said grate comprising: rigid frame means secured to said two walls and comprising a horizontal top support, a horizontal intermediate support, and a horizontal bottom support, said bottom support having a front face and spaced walls rearwardly of said face defining a horizontal upwardly facing slot therein parallel to and rearwardly of said face, said slot in trans verse cross section being of the shape of an inverted,

truncated triangle, said intermediate support having a front face with a horizontal slot extending through .said

support from front to back, said latter slot being elongated in the direction normal to the front to back direction,

said top support having a front face and .an abutment extending forwardly of said face and above said face, said top support having a plurality of bolt openings therethrough from front to back; top spacer means including a plate in juxtaposition to said top support face and having a plurality of pairs of spaced abutments projecting having bolt openings therethrough positioned between each pair of abutments; a plurality of grate bars positioned transversely to said supports and in front .of the spacer means, each bar being between a pair of abutments respectively with the sides of the bar being approximately in contact with the abutments, the bars each having a bottom head of inverted truncated triangular configuration engaged in the slot on the bottom support, each bar having a pocket therein forwardly of the slot in the intermediate support, and a bolt opening from said pocket to said slot, the top of each bar having a wedging face sloping forwardly and downwardly from back to front; bolts extending through the slot of the intermediate support, said openings and into the pocket; nuts in said pockets and secured on said bolts; a top locking bar abutting against said wedging face of .the grate bars and against said abutment; bolts secured in said locking bar and extending rearwardly through the bolt openings in the top support; and nuts secured to the latter bolts rearwardly of the top support.

6. A deflector screen grate for crushers or the like and capable of variable bar spacing, said grate including: a frame means comprising a horizontal top support, a horizontal intermediate support, a horizontal bottom support, and side bars rigidly joining said supports; a plurality of parallel impact bars bridging said sup ports, and means for drawing said bars firmly toward said supports and securing them, said means being adaptable to a variety of positions of said bars on said supports corresponding to different spacings of said bars; and a plurality of sets of spacers for said bars, each set being adapted to space said bars apart on said supports at different spacings from the other set, and each set including upper and lower groups of spacers adapted to be mounted in association with said upper and intermediate supports respectively, said spacers being adapted to engage portions of said bars'to hold the bars in a predetermined spacing with respect to each other with the spacing being determined by the set employed, at least one of said groups comprising a carrier plate and spaced abutments projecting therefrom forming the spacers, said carrier plate being adapted to be supported by the intermediate support and said abutments covering and protecting from wear substantially the entire portion of said intermediate support which would otherwise be forwardly exposed between said bars. 7. A deflector screen grate for crushers or the like and capable of variable bar spacing, said grate including:

a frame means comprising a horizontal top support, a horizontal intermediate support, a horizontal bottom support, and side bars rigidly joining said supports; a plurality of parallel impact bars bridging said supports, and means for drawing said bars firmly toward said supports and securing them, said means being adaptable to a variety of positions of said bars on said supports corresponding to different spacings of said bars; and a plurality of sets of spacers for said bars, each set being adapted to space. said bars apart on said supports at different spacings from the other set, and each set including upper and lower groups of spacers adapted to be mounted in association With said up,- per and intermediate supports respectively, said spacers being adapted to engage portions of said bars to hold the bars in a predetermined spacing with respect to each other with the spacing being determined by the set employed, at least one of said groups comprising a carrier plate and spaced abutments projecting therefrom forming the spacers, said carrier plate being adapted to be supported by the intermediate support and said abutments covering and protecting from wear substantially the entire portion of said intermediate support which would otherwise be forwardly exposed between said bars;

said bars, along the portions of their length between said supports, being of reduced thickness rearwardly to facilitate passage between them of sized frag: ments, but the rear surfaces of said bars in the bear- 6 ing area at said supports, being at least as wide as ,the width of the front faces of the portions of the bars between the supports. 8. A deflector screen grate for crushes or the "like and 5 capable of variable bar spacing, said grate including:

a frame means comprising a horizontal top support, a horizontal intermediate support, a horizontal bottom support, and side bars rigidly joining said supports;

a plurality of parallel impact bars bridging said supports, and means for drawing said bars firmly toward said supports and securing them, said means being adaptable to a variety of positions of said bars on said supports corresponding to different spacings of said bars;

and a plurality of sets of spacers for said bars, each set being adapted to space said bars apart on said supports at difierent spacings from the other set, and each set including upper and lower groups of spacers adapted to be mounted in association with said upper and intermediate supports respectively, said spacers being adapted to engage portions of said bars to hold the bars in a predetermined spacing with respect to each other with the spacing being determined by the set employed, at least one of said groups comprising a carrier plate and spaced abutments projecting therefrom forming the spacers, said carrier plate being adapted to be supported by the intermediate support and said abutments covering and protecting from wear substantially the entire portion of said intermeexposed between said bars;

said bars, along the portions of their length between said supports, being of reduced thickness rearwardly to facilitate passage between them of sized fragments, but the rear surfaces of said bars in the bearing area at said supports, being at least as wide as the Width of the front faces of the portions of the bars between the supports, and being laterally enlarged in the vicinity of the intermediate support to have a width substantially greater than that of the said front faces.

9. A deflector screen grate for crushers or the like and capable of variable bar spacing, said grate including:

a frame means comprising a horizontal top support, a

horizontal intermediate support, a horizontal bottom support, and side bars rigidly joining said supports;

a plurality of parallel impact bars bridging said supports, and means for securing said bars by drawing said bars firmly toward said supports and securing them, said means being adaptable to a variety of positions of said bars on said supports corresponding to different spacing of said bars;

and a plurality of sets of spacers for saidbars, each 'set being adapted to space said bars apart on said supports at different spacings from the other set, and each set including upper and lower groups of spacers adapted to be mounted in association with said upper and intermediate supports respectively, said spacers being adapted to engage portions of said bars to hold the bars in a predetermined spacing with respect to each other with the spacing being determined by the set employed, at least one of said groups comprising a carrier plate and spaced abutments projecting therefrom forming the spacers, said carrier plate being adapted to be supported by the intermediate support and said abutments covering and protecting from wear substantially the entire portion of said intermediate support which would otherwise be forwardly exposed between said bars; 7

said means for securing being releasable and for this purpose being exposed rearwardly of the screen grate while beingprotected by the bars from impact at the forward side of the screen grate.

diate support which would otherwise be forwardly 10. A deflector screen grate for crushers or the like and capable of variable bar spacing, said grate including:

a frame means comprising a horizontal top support, a horizontal intermediate support, a horizontal bottom support, and side bars rigidly joining said supports;

a plurality of parallel impact bars bridging said supports, and securing means for drawing said bars firmly toward said supports and securing them, said means being adaptable to a variety of positions of said bars on said supports corresponding to different spacings of said bars;

and a plurality of sets of spacers for said bars, each set being adapted to space said bars apart onsaid supports at different spacings from the other set, and each set including upper and lower groups of spacers adapted to be mounted in association with said upper and intermediate supports respectively, said spacers being adapted to engage portions of said bars to hold the bars in a predetermined spacing with respect to each other with the spacing being determined by the set employed, at least one of said groups comprising a carrier plate and spaced abutments projecting therefrom forming the spacers, said carrier plate being adapted to be supported by the intermediate support and said abutments covering and protecting from wear substantially the entire portion of said intermediate support which would otherwise be forwardly exposed between said bars;

said securing means including wedging surfaces between one of the end supports and the corresponding ends of the bars to engage said bars and the one end support, and means at the other ends of the bars for simultaneously drawing the said other ends of the bars toward the corresponding support and lengthwise to elfectuate said engagement.

11. A deflector screen grate for crushers or the like and capable of variable bar spacing, said grate including:

a frame means comprising a horizontal top support, a horizontal intermediate support having bolt passage means therethrough, a horizontal bottom support, and side bars rigidly joining said supports;

a plurality of parallel impact bars bridging said sup ports, and securing means for drawing said bars firmly toward said supports and securing them, said means being adaptable to a variety of positions of said bars on said supports corresponding to different spacings of said bars;

and a plurality of sets of spacers for said bars, each set being adapted to space said bars apart on said supports at different spacings from the other set, and each set including upper and lower groups of spacers adapted to be mounted in association with said upper and intermediate supports respectively, said spacers being adapted to engage portions of said bars to hold the bars in a predetermined spacing with respect to each other with the spacing being determined by the set employed, at least one of said groups comprising a carrier plate and spaced abutments projecting therefrom forming the spacers, said carrier plate being adapted to be supported by the intermediate support and said abutments covering and protecting from wear substantially the entire portion of said intermediate support which would otherwise be forwardly exposed between said bars;

said securing means including wedging surfaces between one of the end supports and the corresponding ends of the bars to engage said bars and the one support, clamping means at the other ends of the bars for simultaneously drawing the said other ends of the bars toward the corresponding support and lengthwise to effectuate said engagement, and bolts extending through the passage means of the intermediate support and through said plate and into said bars for drawing the bars firmly against the intermediate support;

' said passage means in the intermediate support being aligned laterally with respect to the intermediate support to receive bolts therethrough at evenly spaced positions in addition to the positions where the bolts are located currently, and said bottom support and said clamping means being constructed to accommodate said bars in the positions corresponding to said evenly spaced bolt positions. 12. A deflector screen grate for crushers or the like and capable of variable bar spacing, said grate including: a frame means comprising a horizontal top support,

a horizontal intermediate support having bolt passage means therethrough, a horizontal bottom sup- 9 port, and side bars rigidly joining said supports;

' a plurality of parallel impact bars bridging said supports, and securingmeans for drawing said bars firmly toward said supports and securing them, said means being adaptable to a variety of positions of said bars on said supports corresponding to different spacings of said bars;

and a set of spacers for said bars, adapted to be mounted in association with said supports to space said bars apart on said supports, and including upper and lower groups of spacers, said spacers being adapted to engage portions of said bars to hold the bars in a predetermined spacing with respect to each other, said set of spacers, comprising a carrier plate and spaced abutments projecting therefrom forming the spacers, said carrier plate being adapted to be supported by the intermediate support and said abutments covering and protecting from wear substantially the entire portion of said intermediate support which would otherwise be forwardly exposed between said bars;

said securing means including wedging surfaces between one of the end supports and the corresponding ends of the bars to engage said bars and the one end support, clamping means at the other ends of the bars for simultaneously drawing the said other ends of the bars toward the corresponding support and lengthwise to effectuate said engagement, and bolts extending through the passage means of the intermediate support and through said plate and into said bars for drawing the bars firmly against the intermediate support;

said passage means of the intermediate support being aligned laterally with respect to said intermediate support to receive bolts therethrough at evenly spaced positions in addition to the positions where, the bolts are located currently, and said bottom support and said clamping means being constructed to accommodate said bars in the positions corresponding to said evenly spaced bolt positions.

13. A deflector screen grate for an apparatus for break, ing rock or the like, said grate including: a frame means comprising a horizontal top support, and a horizontal bottom support, said bottom support having a front face and spaced front and rear Walls rearwardly of said front face defining an upwardly facing slot parallel to and rearwardly of said face, said front wall sloping downwardly and rearwardly toward said rear wall whereby said slot is narrower at the bottom than at the top thereof, said top support having a front face and an abutment extending forwardly of said face and above said face, said top support having bolt openings therethrough from front to back; a plurality of grate bars bridging between said supports and in front of portions of each of the supports, the bars each having a bottom end engaged in the slot on the bottom support, said bottom end having sides defining a wedge corresponding in shape substantially to the shape of the slot between side walls whereby said bars are wedged into said slot, a top locking bar abutting against a part of the grate bars at the top thereof and 9 against said abutment; and bolts secured in said locking bar and extending rearwardly through the bolt openings; the combustion of the abutment, the locking bar, and the grate bar tops being such that tightening said bolts thrusts the grate bars downwardly to force said wedge ends se- 5 curely into said slot and to force the grate bars rearwardly against said portions of the supports.

References Cited by the Examiner UNITED STATES PATENTS 1,048,721 12/1912 Morgel 209395 2,767,928 10/1956 Hanse 24185 HARRY B. THORNTON, Primary Examiner.

HERBERT L. MARTIN, Examiner. 

5. IN A CRUSHER FOR ROCK OR THE LIKE COMPRISING WALL DEFINING A BREAKING CHAMBER, A DEFLECTOR SCREEN GRATE IN SAID CHAMBER, AND AN IMPELLER IN SAID CHAMBER EXTENDING BETWEEN TWO WALLS AND ROTATING IN A GIVEN DIRECTION ABOUT A GENERALLY HORIZONTAL AXIS TO THROE ROCK AGAINST SAID GRATE, THE IMPROVEMENT IN SAID GRATE COMPRISING: RIGID FRAME MEANS SECURED TO SAID TWO WALLS AND COMPRISING A HORIZONTAL TOP SUPPORT, A HORIZONTAL INTERMEDIATE SUPPORT, AND A HORIZONTAL BOTTOM SUPPORT, SAID BOTTOM SUPPORT HAVING A FRONT FACE AND SPACED WALL REARWARDLY OF SAID FACE DEFINING A HORIZONTAL UPWARDLY FACING SLOT THEREIN PARALLEL TO AND REARWARDLY OF SAID FACE, SAID SLOT IN TRANSVERSE CROSS SECTION BEING OF THE SHAPE OF AN INVERTED TRUNCATED TRIANGLE, SAID INTERMEDIATE SUPPORT HAVING A FRONT FACE WITH A HORIZONTAL SLOT EXTENDING THROUGH SAID SUPPORT FROM FRONT TO BACK, SAID LATTER SLOT BEING ELONGATED IN THE DIRECTION NORMAL TO THE FRONT AND BACK DIRECTION, SAID TOP SUPPORT HAVING A FRONT FACE AND AN ABUTMENT EXTENDING FORWARDLY OF SAID FACE AND ABOVE SAID FACE, SAID TOP SUPPORT HAVING A PLURALITY OF BOLT OPENINGS THERETHROUGH FROM FRONT TO BACK; TOP SPACER MEANS INCLUDING A PLATE IN JUXTAPOSITION TO SAID TOP SUPPORT FACE AND HAVING A PLURALITY OF PAIRS OF SPACED ABUTMENTS PROJECTING FORWARDLY THEREFROM; INTERMEDIATE SPACER MEANS IN JUXTAPOSITION TO SAID INTERMEDIATE SUPPORT FACE AND HAVING A CORRESPONDING PLURALITY OF PAIR OF SPACED ABUTMENTS PROJECTING FORWARDLY THEREFROM, SAID INTERMEDIATE SUPPORT HAVING BOLT OPENINGS THERETHROUGH POSITIONED BETWEEN EACH PAIR OF ABUTMENTS; A PLURALITY OF GRATE BARS POSITIONED TRANSVERSELY TO SAID SUPPORTS AND IN FRONT OF THE SPACER MEANS, EACH BAR BEING BETWEEN A PAIR OF ABUTMENTS RESPECTIVELY WITH THE SIDES OF THE BAR BEING APPROXIMATELY IN CONTACT WITH THE ABUTMENTS, THE BARS EACH HAVING A BOTTOM HEAD OF INVERTED TRUNCATED TRIANGULAR CONFIGURATION ENGAGED IN THE SLOT ON THE BOTTOM SUPPORT, EACH BAR HAVING A POCKET THEREIN FORWARDLY OF THE SLOT IN THE INTERMEDIATE SUPPORT, AND A BOLT OPENING FROM SAID POCKET TO SAID SLOT, THE TOP OF EACH BAR HAVING A WEDGING FACE SLOPING FORWARDLY AND DOWNWARDLY FROM BACK TO FRONT; BOLTS EXTENDING THROUGH THE SLOT OF THE INTERMEDIATE SUPPORT, AND OPENINGS AND INTO THE POCKET; NUTS IN SAID POCKETS AND SECURED ON SAID BOLTS; A TOP LOCKING BAR ABUTTING AGAINST SAID WEDGING FACE OF THE GRATE BARS AND AGAINST SAID ABUTMENT; BOLTS SECURED IN SAID LOCKING BAR AND EXTENDING REARWARDLY THROUGH THE BOLT OPENINGS IN THE TOP SUPPORT; AND NUTS SECURED TO THE LATTER BOLTS REARWARDLY OF THE TOP SUPPORT. 